The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The power consumption and the constriction size are critical and must therefore be minimized for the use of a clutch of this type in the drivetrain of a power vehicle. There are also further demands: Such a wide regulation range of the transmitted torque that non-slip starting off from a stationary position is possible, on the one hand, and complete separation is (also) possible for noise reasons, on the other hand; and finally fast response to be compatible with electronic driving dynamic controls (ESB, ABS, etc).
A clutch of this type is known from EP 940 286 A2. The magnetic field is generated by a coil fixed with respect to the housing here. An air gap thereby arises between its yoke and the rotating parts, in particular the disks, which has to have a substantial width for tolerance reasons. The magnetic field lines are thereby interrupted and the magnetic field acting on the magnetorheological fluid is substantially weakened. Furthermore, the field lines are relatively long due to the construction of the magnetic coil with its yoke, which further reduces the size of the active part of the magnetic field, that is its part acting on the magnetorheological fluid.
It is furthermore known from EP 940 286 A2 (FIGS.5 and 6) that, at both sides of the clutch, two yokes, of which one is provided with a magnetic coil, form an end face parallel to the disks. The magnetic field passes through the disks, and indeed in the outer region in a magnetic flux direction and in the inner region in the opposite direction. Accordingly, the disks are separated from one another by zones of low magnetic permeability extending in the peripheral direction to prevent a magnetic short-circuit. These zones can be provided by complex and therefore expensive metallurgical measures. In practice, however, they are slits which weaken the disks in the peripheral direction and in the centrifugal direction. This is undesired for a clutch in the drivetrain of a motor vehicle.